• Some overdue upgrades

    Martin Cejp11/25/2021 at 22:45 0 comments

    In the initial prototype, the bare reed switch (its enclosure being made of glass!) was just taped to the frame next to where the magnet passes; fortunately there was not much rain or mud, since this 'solution' would have fallen apart pretty fast. The switch was soldered directly to the cable harness, with no possibility of disconnection. This is now history.

    I am now using a factory-sealed sensor and I crimped an IP67-compliant connector to ease maintenance.

    (Disclaimer: this project is not being sponsored by EDAC in any way :)The mounting of the sensor has also been greatly improved. A 3D-printed spacer now delimits the position of the sensor with respect to the bicycle frame. In retrospect, a rigid spacer was not a very good engineering solution, because it does not provide flexibility in fine-tuning the sensor head positioning at mounting time. But, for the time being, it will do.
    More news coming soon!

  • Connectors!

    Martin Cejp11/18/2021 at 21:16 0 comments

    While the initial cardboard-box prototype has been quite a success, clearly for long-term reliability, waterproof enclosures and connections will be required. I have ordered samples of several connectors to evaluate their fitness for this project.

    To connect the reed switch sensor, I decided to try out the EDAC 560. Rated IP67, this should provide more than sufficient protection from the environment -- assuming correct crimping. These are only available in a wire-to-wire variant, and they have a disadvantage: it is not really possible to apply strain relief for the individual wires near the connector.

    The second sample is the Weipu SP13, a wire-to-wire, soldered variant. Its clones are abundant on sites such as Aliexpress, but I decided to try the original due to its good availability. This is a 4-pin version, which I wanted to use for connecting the front I2C bus (which carries the OLED screen and, in the future, buttons via a port expander). It feels very well-made, however, as expected, it is quite large, so I will not use it at the moment. Instead, I will try to get my hands on a pair of Weipu's miniature SA6 series (these are 6mm aluminium connectors)

    Finally, a pair of 14-pin TE AMPSEAL connectors (1-776262-1 + 776273-1). And boy, are they massive. A wire-to-panel combination, these were candidates for the connection between the "ECU" and the cable harness, but I think I will instead go for the more compact SP21 (21mm round plastic connector). I will need about 10 pins for version 2 of the project, so the AMPSEAL would be an unnecessary overkill (the only smaller variant is 8 pins).

  • OLED housing print #1 -- review

    Martin Cejp10/16/2021 at 13:24 0 comments

    Printed with Prusa i3 MK3, eSUN PLA+ Filament 1.75mm, 0.2mm layer thickness.

    • LCD opening should be a bit larger (~0.5 mm each side) to accommodate viewing angles; probably should be chamfered as well
    • interior slightly too small (~0.5 mm in each axis), making the PCB rotate a bit
    • opening for connector should be 1.6 mm to match PCB thickness (instead of 1.0 mm)
    • opening for connector could be ~1 mm narrower
    • 2.0 mm thickness should be enough for walls (instead of 2.5 mm)
    • apparently STL was in millimeters. mistake in export from Blender?
    • next prototype should incorporate holes for screwing the PCB in
    • thanks, Nuno!